1. Field of the Invention
The present invention relates to a lock as described in the preamble to claim 1 which includes a housing and a pull absorbing strap.
2. The Prior Art
U.S. Pat. No. 4,074,916, incorporated herein by reference, discloses such a lock wherein the strap is constituted by a wire or a cable. In this patent it is described how safety is increased against a person being able to release the lock by pulling the wire while simultaneously the wire is turned or rotated about its longitudinal axis. In this prior art lock, the locking device for the wire is a disc that isxe2x80x94by means of a spring fitted in the cavity between the sidewalls of the housingxe2x80x94pressed against the entry openings for the free end of the wire. Hereby the spring ensures that the disc will always wedge securely in order to tightly nip in the wire it if is attempted to pull out the wire through the entry opening. If, conversely, the wire is pulled in the opposite directionxe2x80x94out through the exit opening for the wire, the spring yields and the wire is able to pass freely. When thus the one end of the wire is secured in the lock housing and the opposite end is pulled through the housing, a closed wire loop is obtained that cannot be opened, but only be tightened. Locks of this type are used for a variety of sealing purposes, e.g., for sealing of large transport containers. Once the lock has been tightened, it cannot be removed unless the wire or the lock is damaged.
The U.S. patent disclosure teaches that, in advance, the wire or the cable has been pressed flat to bring about an oval cross section. Besides the lock housing is provided interiorly with such configuration that said turning or rotation of the wire becomes difficult, the housing along with the disc forming support areas intended to prevent such turning. Albeit the U.S. patent disclosure does not mention the wire configuration in detail, it seems, however, that it is the case of a conventional wire formed by helical winding of a number of metal wires. In order to accomplish said oval cross section, a difficult pressing operation is thus required that uses a complex pressing tool.
It is the object of the present invention to provide an improved lock that is both reliable and inexpensive and that does not presuppose initial flat-pressing of a wire. The lock being a disposable device sold in large numbers, even a minor reduction in the production costs is important, and thus the invention makes it possible to eliminate the need for a complex pressing tool.
This is obtained by a lock of the kind described above, wherein the strap is a string of a plastics material and having a polygonal cross section. Besides, particularly advantageously the locking device can have a toothed or/and rough surface. This also means that it is possible, in a simple manner, to ascertain visually whether attempts have been made to break the lock, since such attempt will translate into damage to the strap surface. xe2x80x9cPolygonalxe2x80x9d as used herein designates both a convex and a concave polygon, while it is expected, however, that a string with a convex polygonal cross section will be simpler to manufacture. The string can, in cross section, have sides of equal size and the string can, in cross section, have slightly rounded corners.
The housing and the locking device can, in a conventional manner, be configured as featured in claim 2 where the housing has an interior, sloped wall that forms a guide for the locking device that is preferably configured for being able to roll along this wall.
The support areas of the housing can be formed in a variety of ways, including the way featured in claim 3, by the entry opening for the strap having a cross section that is complementary with the polygonal cross section of the strap. Preferably, in the nipping area for the strap, an interior wall in the housing may be provided with a track shaped in accordance with the cross section of the strap. Advantageously it can be a ridged indentation whereby a portion of the strap can be received in the guide between the wall and the locking device and secured against said turning when the strap is oriented by a nipping force oriented perpendicular to axial direction and exerted by the locking device. It will be understood that in that case the support face of the locking device will constitute a part of the support areas that serve to prevent turning.
Particularly advantageously the strap can be reinforced, eg with fibres that are distributed in the plastics material or by a central, longitudinally extending core of metal that can be manufactured in a conventional manner by twisting of metal wires. In that event the strap can advantageously be manufactured by extrusion.
The entry opening, ie the first opening of the housing, and the exit opening, ie the second opening of the housing, for the strap as featured in claim 10 having particular linear guides for the strap, it is possible to apply to the strap, during its advancement through the cavity within the housing, to a resilient flexing, the upwardly oriented momentum of which urges the strap towards the locking device.
Hereby it is thus ensured that the locking device will, by any movement of the strap towards the entry opening, be firmly wedged between the strap and the sloping wall. Simultaneously it is possible to altogether omit a separate resilient body, the resilient effect of a slightly flexed strap being used to ensure a nipping force between the locking device and the strap. This effect is obtained in the linear guides being, at the entry and/or exit opening (5), oriented towards one surface of the locking device. Hereby it is ensured that the strap cannot pass through the cavity of the housing from the entry opening to the exit opening without having to flex. U.S. Pat. No. 3,770,307 teaches a corresponding solution.
As featured in claim 11 the locking device can conveniently be a substantially circular metal disc or roller with the rough or toothed surface along the circle periphery. Such locking device is extremely simple to manufacture.
In accordance with an embodiment according to claim 12, the linear guide of the entry directs the strap towards a tangent of the locking device and the linear guide of the exit directs the strap towards a chord of the locking device.
In accordance with an embodiment according to claim 13, the lock is particularly simple to manufacture.
Additionally, the lock may conveniently be configured as featured in claim 14. Hereby a high degree of symmetry is accomplished which is advantageous from a technical production point of view and, besides, it is possible for the end user himself to mount the first end of the strap in the lock.